This invention relates to sound reproduction for motion picture systems and, more particularly, it concerns improvements in audio components for use in motion picture cameras of a type adapted to receive a cassette containing separate photographic film and audio tape strips guided to respective camera mounted photographic and audio stations to and from common takeup and supply spools within the cassette.
In a commonly assigned copending application Ser. No. 869,131, filed Jan. 13, 1978, in the name of E. H. Land et al, several alternative embodiments of a multi-purpose film cassette are disclosed in which a photographic film strip and a magnetic audio tape are interwound in alternate convolutions on supply and takeup spools rotatably supported within the cassette. The respective strips are guided in separate paths between the spools to pass in operative relationship through photographic and audio stations defined in part by the cassette and in part by the recording camera and playback projector designed to receive the cassette. The organization of components and the operation of same at the photographic station are now well known and physically embodied in the motion picture system available commercially under the name "POLAVISION," a registered trademark of Polaroid Corporation, Cambridge, Massachusetts. The audio station, however, has not been incorporated in a commercial embodiment of the system to date.
Prior to the development represented by the disclosure of copending application Ser. No. 869,131, motion picture systems of the aforementioned type have been adapted for sound by providing the film strip with a relatively narrow marginal strip of magnetic material for receiving an audio signal. An example of such a system is disclosed in U.S. Pat. No. 3,848,977, issued Nov. 19, 1974 to Donald T. Scholz and assigned to the assignee of the present invention. A principle advantage resulting from the use of separate photographic film and audio tape strips, as compared with a film strip mounted audio signal carrier, is that the separate audio tape provides increased audio signal capacity needed for high fidelity sound reproduction. Full attainment of high fidelity sound reproduction consistent with the capacity of the separate audio tape, however, has required solution to problems encountered with achieving the physical characteristics of components required to record quality audio signals on the magnetic tape strip particularly in the recording camera. It is important, for example, that the audio components are essentially free of vibrations to avoid tape flutter and other undesirable noise creating characteristics. Because of the need at the photographic station for oscillating or reciprocating components to incrementally advance the film strip, the audio components must be completely isolated from vibration developed by such components of the photographic station. In addition, the audio tape must be advanced in complete synchronism with the film strip and must be capable of repeated start and stop operation peculiar to amateur cinematography. Finally, the audio components of the camera must not interfere in any way with simple loading of the cassette into the camera and must, therefore, be arranged for automatic positioning in relation to the cassette-contained audio tape.